Modified montmorillonite clay catalyst

ABSTRACT

A modified montmorillonite clay is prepared by heating it, impregnating it with an organic liquid, acid-activating it with a strong acid, and then washing it with water until it is substantially free of acid anions. The modified clay is useful as a catalyst, particularly for the preparation of tetrahydrofuran/alkylene oxide copolymers.

DESCRIPTION

1. Technical Field

This invention relates to a modified clay and to its use as apolymerization catalyst. It is more particularly directed to a modifiedmontmorillonite clay and to its use as a catalyst in the polymerizationof tetrahydrofuran (THF) and an alkylene oxide (AO).

2. Background Art

Processes for catalytically preparing THF/AO polymerizates usingmontmorillonite clays as catalysts are known. One such process is shownin U.S. Pat. No. 4,127,513 to Howard Edward Bellis. According to theBellis process, THF and an AO are catalytically polymerized using as thecatalyst a montmorillonite clay which has been acid activated so that itcontains, per gram, 0.1-0.9 milliequivalent of hydrogen ions havingpK_(a) values of -3 to -8.

While the Bellis clay catalyst is quite satisfactory, it has been foundthat the clay catalyst of the present invention can provide apolymerization rate higher than that of Bellis, with its accompanyingbenefits, and with less color formation in the product during the earlystages of polymerization. In addition, the clay catalyst of theinvention has greater physical strength than that of Bellis so that itcan be used with less physical degradation and attrition.

The clay catalyst of the invention is prepared from a type of naturallyoccurring granular sodium montmorillonite clay known as Wyomingbentonite. A clay of this class, "KWK Volclay" bentonite, is sold byAmerican Colloid Company of Skokie, Illinois. "Granular", in thiscontext, defines a particulate clay 90% of which passes through a 20mesh U.S. Sieve (-20 mesh), but is retained on a 70 mesh U.S. Sieve (+70mesh).

The clay catalyst of the invention is prepared by first holding the claystarting material (raw clay) at a temperature of 300°-600° C. for about1-20 hours, in air, preferably 450°-550° C. for 2-6 hours.

The thus heat-treated clay is next impregnated with an organic liquidwhich is capable of being intercalated into the clay and finding its wayinto the clay's interstices. Illustrative of organic liquids which canbe used are THF, p-dioxane, and ethers such as diethyl ether and dibutylether. THF is preferred. Impregnation can be accomplished by anyconventional technique, but is preferably done by simply stirring theclay in the liquid at a temperature of about 0°-60° C., preferably20°-25° C. This treatment is continued until no more liquid is taken upby the clay, as determined visually. The time required to complete theimpregnation step will vary with the temperature of the liquid and theparticle size of the clay, but will in most cases be 4-20 hours.

The thus impregnated clay is then optionally stripped of residualorganic liquid, "residual" being defined as that liquid which is notentrained by the clay. The stripping is done by first separating theclay and the liquid by decantation, filtration or centrifugation, andthen passing air at ambient temperature through the clay until the clayparticles no longer cohere.

The stripped clay is then acid-activated. This is done by bringing theclay into contact with 5-30%, preferably 10-20%, by weight, of aqueoushydrochloric acid for 1-18 hours at a temperature of about 20°-100° C.The acid-activation is ordinarily accomplished by immersing the clay ina bath of acid, with gentle stirring, until the activation is complete,as is well known in the art. Any strong acid such as nitric, sulfuricand phosphoric (all forms) can also be used to activate the clay.

The clay is then separated from the acid solution by decantation,filtration of centrifugation, and is washed with water, preferablydistilled or deionized water, until it is substantially free of acidanions. "Substantially free" means that most of the anions have beenremoved, only a small insignificant number remaining. When hydrochloricacid is used, this point is determined by adding aqueous silver nitratesolution to the wash water effluent and then visually inspecting theeffluent for silver chloride precipitate.

If desired, the clay can then be dried by heating it. The temperature ispreferably held below about 150° C. to maintain its high activity. It ispreferred that the catalyst be subjected to the drying step becausewater functions as a chain terminator in the THF/AO polymerization andits presence in the catalyst may therefore affect the polymerizationadversely.

The clay catalyst thus prepared, with or without the drying step, can beused directly in the polymerization of THF and an AO.

The THF used in the polymerization can be any kind ordinarily used toprepare THF/AO polymers.

The AO used can be any containing two or three carbon atoms in its oxidering. It can be unsubstituted or substituted with, for example, alkyl oraryl groups, or with halogen atoms. Illustrative of such alkylene oxidesare ethylene oxide; 1,2-propylene oxide; 1,3-propylene oxide;1,2-butylene oxide; 1,3-butylene oxide;3,3-bischloromethyl-1,3-propylene oxide; styrene oxide andepichlorohydrin.

The polymerization is carried out by first preparing a 5-20%, by weight,slurry of the clay catalyst in THF. A mixture of THF and an AO is thenprepared, with the THF and oxide present in such proportions to oneanother as will give a copolymer with a THF/AO weight ratio of20-80/80-20, preferably 60-65/40-35.

To this mixture is added 0.2-6%, by weight, of a chain terminator.Enough of the resulting THF-AO-chain terminator mixture is then added tothe clay slurry to give a clay concentration of about 3-25%, preferably5-20%, by weight, in the mixture. Illustrative of chain terminatorswhich can be used are water, 1,4-butanediol, ethylene glycol,1,6-hexanediol, trimethylolpropane, glycerine and pentaerythritol.

This reaction mass is then held at 40°-90° C., preferably 68°-80° C.,with constant stirring, until a polymerizate having the desiredmolecular weight is obtained, as determined by periodic sampling andspectroscopic analysis. This ordinarily requires a reaction time of10-240 minutes.

The clay is then separated from the reaction mass by filtration,decantation or centrifugation, and unreacted THF is separated from themixture by distillation, leaving the THF/AO polymerizate behind.

The THF/AO polymerization is preferably run in a continuous fashion.When run this way, the same relative amounts of catalyst and reactants,and the same temperatures and reaction times are used as in the batchmode. A slurry of clay is first prepared in a 50-60%, by weight,solution of batch-prepared THF/AO polymerizate in THF. This slurry isstirred, heated to the reaction temperature and held there, withstirring, while a mixture of THF, AO and chain terminator, in thedesired proportions, is slowly added to it. The clay catalyst can beheld in the reaction zone by suitable filters or screens. After asuitable residence time, the product, a THF/AO polymerizate, iswithdrawn from the reaction zone.

While the clay catalysts of the invention will confer their greatestbenefits when used to catalyze the polymerization of THF and AO, theycan also be used to catalyze any reaction normally catalyzed bymontmorillonite clay, e.g., the reaction of methanol and isobutylene toform methyl-t. butyl ether.

EXAMPLES

In the following examples, all parts are by weight.

EXAMPLE 1 --Best Mode

Ten parts of granular Volclay KWW, U.S. Sieve -10 +35, was held at 500°C. for 3 hours. The clay was then cooled to ambient temperature andimmersed in THF at 20°-22° C. for 16 hours. At the end of the immersionperiod, the clay was separated from the THF by vacuum filtration to givea light-colored, free-flowing granular product.

This product was added to 30 parts of 20% hydrochloric acid and stirredgently for 3 hours at 60°-80° C. The slurry was then cooled to ambienttemperature, allowed to settle, and the acid decanted.

The clay was then added to 30 parts of deionized water, stirred gentlyfor about 10 minutes, and the water decanted. This washing step wasrepeated until the water effluent gave no precipitate when tested withsilver nitrate solution.

The clay was then dried at 100° C. for 5 hours, and was ready for use asa catalyst.

EXAMPLE 2

(1) Into a reactor having a reflux condensor and an overflow tube wereplaced 150 parts of the clay catalyst of Example 1.

(2) Seven hundred fifty parts of a 56% solution of batch-preparedTHF/ethylene oxide polymerizate in THF were prepared according to theprevious description.

(3) The solution of (2) was added to the reactor of (1), and theresulting slurry was heated to and held at 70° C., with stirring.

(4) A feed soluton containing

ethylene oxide:1320 parts

water:99 parts

THF:5180 parts

was added to the slurry of (3), with gentle stirring, at the rate of18-20 parts per minute.

The polymerizate product was recovered from the reactor as overflow atthe rate of 18-20 parts per minute. The THF/ethylene oxide copolymer inthe polymerizate contained 49 mol percent of ethylene oxide units.

INDUSTRIAL APPLICABILITY

The THF/AO polymers produced by processes using the clays of theinvention as catalysts can be used to prepared polyurethanes accordingto methods well known in the art.

I claim:
 1. A catalyst material prepared by(a) holding a raw granularWyoming bentonite at a temperature of about 300°-600° C. for about 1-20hours, in air; (b) impregnating the product of (a) with an organicliquid capable of being intercalated into said product; (c) optionally,removing residual organic liquid from the product of (b); (d) activatingthe product of (b) or (c) with a strong acid; (e) removing residual acidfrom the product of (d); (f) washing the product of (e) with water untilit is substantially free of acid anions; and then (g) optionally, dryingthe product of (f) at a temperature below about 150° C.
 2. The catalystmaterial of claim 1 in whose preparation the acid is step (d) ishydrochloric acid.
 3. The catalyst material of claim 1 in whosepreparation the organic liquid in step (b) is tetrahydrofuran.
 4. Acatalyst material prepared by(a) holding a raw granular Wyomingbentonite at a temperature of about 300°-600° C. for about 1-20 hours,in air; (b) impregnating the product of (a) with tetrahydrofuran; (c)optionally, removing residual tetrahydrofuran from the product of (b);(d) activating the product of (b) or (c) with hydrochloric acid; (e)removing residual acid from the product of (d); (f) washing the productof (e) with water until it is substantially free of chloride ions; andthen (g) optionally, drying the product of (f) at a temperature belowabout 150° C.